Cementitious compositions are used for filling, backfilling and stabilization in a large variety of situations. In particular, at mining sites, for safety and other reasons, it is frequently necessary to conduct backfilling operations, or to stabilize or solidify mine wastes at the surface. Conventionally, Portland cement is used for this purpose; however, having regard to the high cost of this material, and of shipping it to the intended use site, this represents a major cost in mining operations throughout the world, and in Canada in particular. Any reduction in the amount of Portland cement required would lower the operating costs of a mine and contribute to the profitability of the mining operation. Similarly, in other filling and backfilling operations, any reduction in the use of Portland cement and its replacement by more readily available or cheaper materials would provide an immediate economic benefit for the subject operation.
In the context of mining operations, one material that has recently been considered as having the potential for reducing the amount of Portland cement used is slag, and in particular non-ferrous granulated slag, which is a readily available waste product of the smelting of copper and nickel concentrates. However, in order to use any material to replace Portland cement, it is necessary that the cementing (pozzolanic) properties be substantially equivalent to those of Portland cement. Although many forms of slag contain suitable constituents, it is difficult to activate the cementing properties of the slag.
Activation of the pozzolanic properties of a non-ferrous granulated slag requires the addition of cementing supplements as an activator, to provide the calcium, sulphur and aluminum needed to grow the cementitious mineral ettringite. Ettringite has the composition Ca6Al2(SO4)3(OH)12×26H2O and is the first binder to form in a cement. To form ettringite, conventionally calcium is supplied by quick lime, sulphur by gypsum and aluminum by supplements such as fly ash and a calcium aluminate slag obtained from the recycling of spent catalysts.
Currently, using conventional methods, there are three approaches to activating non-ferrous granulated slag. The first method is to add the cementing supplements at the smelter just prior to granulation, as disclosed by Philip et al. in U.S. Pat. No. 4,756,761 and R. J. Atkinson et al. (1989, Using Smelter Slag in Mine Backfill, Mining Magazine, Vol. 160, No. 8, pp. 118-123). The second method is to blend the non-ferrous granulated slag with Portland cement as disclosed by Krofchak in U.S. Pat. No. 6,033,467; however, this method suffers from the disadvantage noted above, associated with the use of Portland cement as the activator. The third method is to add one or more cementing supplement during mixing with the aggregate material.
For the third method, it is known to use a composition containing fly ash waste as its main ingredient. Fly ash waste is available as a by-product from the combustion of coal in thermal power plants. However there are a number of drawbacks to using fly ash as an activator, including issues of quality, transportation and availability. The pozzolanic properties of fly ash vary according to the type of coal from which it was created, which creates a serious problem of inconsistency and unreliability of performance. In some instances, the fly ash does not provide sufficient amounts of aluminum for ettringite nucleation and growth. Fly ash is not locally available at most of the non-ferrous smelters and mining operations, particularly in Canada, so for such applications it must be shipped at considerable expense.
It is also known to use calcium aluminate to supply aluminum for ettringite nucleation and growth. However, there are very limited sources for the compound, and transportation costs of shipping it to the intended use site may be prohibitively high, or at least significantly increase operating costs.
Therefore, what is needed is a novel, readily available and affordable activator for activating pozzolanic materials, such as slag, to form cementitious compositions which can be used to replace Portland cement in filling and backfilling operations, in particular for backfilling of underground mine workings and the stabilization and solidification of mine wastes, and which compositions do not suffer from the disadvantages of the known compositions, including those noted above.
It has now been found that feldspar materials can be used as an effective and affordable activator of many types of pozzolanic materials, preferably particulate materials, and including especially slag materials, either ferrous or non-ferrous, and in granulated or other form; and further including fly ash having minimal self-cementing properties, and siliceous rocks.